EventScreen

Continuing work on the event screen:
 - Added listener methods to the save and delete buttons (MJ will need
to implement those methods in the EventScreenPresenter)
 - Added the proper buttons to the event screen depending on the user
and whether it is a new event or not
 - Fixed an issue with the fields in a new event being uneditable
 - Began work on saving the contents from the EventScreen in an event
so it can be saved.